In order to understand the mechanism of HIV-1 gene regulation, we have tried to map the positive and negative regulating regions of LTR and define their role(s)in HIV-1 gene transcription. Negative regulatory elements (NRE) of HIV-1 LTR are known to be involved in the down-regulation of HIV gene expression, whereas enhancer-TAR region is implicated in binding with transcriptional activators such as NF-kB, TAT, SP-1 etc. Earlier, we reported a DNA-binding protein that interacts with a distinct 30 base pair DNA segment within the NRE region and which exhibits a strong transcriptional inhibitory activity in the in vitro HIV-LTR directed transcription. Recently, we also determined the presence of a nuclear matrix attachment region (MAR) within the NRE that recognizes a sequence-specific DNA-binding nuclear matrix protein (NMP). This partially purified NMP from HIV-1 infected T-cells (HUT-78) and monocytes (THP-1) exerts an inhibitory effect on NF-kB binding activity in in vitro binding assays, suggesting the role of NRE's and NMP's in HIV-1 gene regulation. (Nuc Acids Res 24:1895, 1996). c-erbB-2/HER-2/neu gene is overexpressed and amplified in many solid tumors by specific DNA-protein interactions. We have reported a sequence-specific DNA-binding protein that is present exclusively in the human breast biopsy samples extracts. Microinjection of the affinity purified protein induces mitogenesis in resting NIH/3T3 cells and the cell surface expression of the c-erbB-2 protein. Polyclonal antibodies are raised against gel purified HER promoter binding factor (HPBF). In situ studies are in progress. We have recently extended our studies to the binding domains of nuclear matrix proteins (NMPs). NMPs are known to participate in many key biological reactions. We have identified a novel sequence-specific NMP from extacts of malignant breast tissues which recognize a distinct promoter segment of c-erbB-2 gene. We have already semi-purified the NMP protein from an erbB-2 promoter DNA affinity column, which shows a sequence-specific DNA binding activity towards this segment of c-erbB-2 promoter. Further characterization of this protein is in progress. To evaluate the role of c-erbB-2 gene in prostate cancer progression, we initiated studies in the area of hnRNPs, which are known to be involved in RNA transcription, processing and splicing reactions. Our results indicate a sequence-specific hnRNP protein that recognizes a distinct segment of c-erbB-2 gene promoter.